Clarifiers are an integral part of the activated sludge process—crucial components that often determine the success or failure of the entire treatment system.
The performance and capacity of a center-feed clarifier is very sensitive to the intensity of influent jets entering into the clarifiers. A center-feed clarifier naturally generates a strong influent jet due to its small center-feed area in a circular clarifier tank as shown in FIG. 1. The intensive center influent often brings significant turbulence into the settling compartment, especially under high flow conditions. To enhance the hydraulic efficiency and capacity of center-feed clarifiers, one of the most important key issues is to develop a center-feed apparatus, which could be used to effectively reduce the intensity of the central influent jet and turbulence under high-flow conditions.
Various types of energy dissipating devices have been developed for dissipating the energy of the influent entering into a flocculation well in the center-feed clarifiers. As shown in FIG. 2, the traditional Energy Dissipating Inlet (EDI) has often been used in many recent clarifier designs with the center-feed structure in order to dissipate the clarifier inlet energy. Using the traditional EDI shown in FIG. 2, the jet of clarifier influent flow through a few influent ports is still very strong due to the small cross sectional area of the ports, especially in a large clarifier and under high flow conditions. If the cross sectional area of the inlet ports is simply enlarged, flow short-circuiting (or unevenly distributed flow) may occur among the ports due primarily to the insufficient resistance along the radius.
An apparatus with similar principle but different flow controls was also invented by Write (U.S. Pat. No. 6,800,209, Oct. 5, 2004). His EDI has a single layer column centered in the clarifier and closed at the bottom. Ports in the wall of the column are each equipped with a pair of hinged gates on the sides of the center vane and a bottom baffle underlying the port. The gates can direct the influent flows in opposite tangential directions from each port into impingement.
Esler et al. invented an energy dissipating devise (U.S. Pat. No. 6,276,537) which is consists of a single layer column and closed at the bottom. His EDI is equipped with pipes that extend from the bottom of the column and direct the flow that discharges from the EDI in opposite directions. The strong influent jet impingement occurs either outside the wall of the EDI (Write, 2004) or underneath the bottom of the EDI (Esler, et al., 2001).
The turbulence in clarifiers must be lowered in order to control the dispersed sludge blanket. Any EDI alternatives having either the intensive inlet jets or the strong flow impingement among the jets occurred outside the EDI column may not be able to effectively confine the turbulence entering into clarifiers.
To produce satisfactory hydraulic behavior, one of the necessary design conditions is that the cumulative space of the inlet ports of an EDI must be big enough. However, this condition alone is not sufficient to guarantee a low momentum entering into the clarifiers.
An optimized design of clarifier inlet structure should simultaneously satisfy both the working principles, i.e. a large accumulative space of inlet ports and a uniform flow distribution among the inlet ports in the outside wall of EDI. An innovative “Multilayer Energy Dissipating Inlet Column” (MEDIC) could be used as an effective solution to the problem of strong center-feed jets.